Environmental regulations have called for increasing emission limits that require reduction in the NOx and PM from diesel combustion processes, and in particular from diesel compression engines. While diesel particulate filters (DPF) are capable of achieving the required reductions in PM, which is typically carbonaceous particulates in the form of soot, there is a continuing need for improved systems that can provide the required reductions in NOx, often in connection with the particulate matter reduction provided by a DPF.
In this regard, systems have been proposed to provide a diesel oxidation catalyst (DOC) upstream from a DPF in order to provide an increased level of NO2 in the exhaust which reacts with the soot gathered in the DPF to produce a desired regeneration of the DPF (often referred to as a passive regeneration). However, such systems become limited at temperatures below 300° C. and typically produce a pressure drop across the oxidation catalyst that must be accounted for in the design of the rest of the system. Additionally fuel, such as hydrogen or hydrocarbon fuel, can be delivered upstream of the DOC to generate temperatures greater than 600° F. in the DPF (often referred to as active regeneration).
It has also been proposed to include a burner within such systems to ignite and combust fuel in the exhaust downstream from the diesel combustion process to selectively increase the temperature for exhaust treatment processes downstream from the burner. Examples of such proposals are shown in commonly assigned and co-pending U.S. patent application Ser. No. 12/430,194, filed Apr. 27, 2009, entitled “Diesel Aftertreatment System” by Adam J. Kotrba et al, the entire disclosure of which is incorporated herein by reference.
While current burners for such systems may be suitable for their intended purpose, there is always room for improvement. For example, the pressure drop and/or back pressure associated with such burners is always important when other exhaust treatment devices are included in the system, as is thermal mixing of the exhaust exiting such a burner so that potentially damaging hot spots can be removed from within the exhaust flow exiting the burner and a reasonably uniform exhaust temperature profile can be provided to the downstream portion of the system.